Disadvantages of precast concrete pdf

A similar bridge on this river was fabricated ashore and pushed across its pylons. The Martel bridge was adopted by the British Army in 1925 as the Large Box Disadvantages of precast concrete pdf Bridge. A scaled down version of this design, the Small Box Girder Bridge, was also formally adopted by the Army in 1932.

The United States was another country whose army created their own copy, designating it the H-20. Both the Large Box and Small Box designs would go on to see much service in World War II, especially in the case of the latter. 1960s, especially in the West, and many new bridge projects were in progress simultaneously. Most of the bridges still under construction at this time were delayed for investigation of the basic design principle. Some were abandoned and rebuilt as a different form of bridge altogether. Some bridges were strengthened a few years after opening and then further strengthened years later, although this was often due to increased traffic load as much as better design standards. 1970 was strengthened in 1970 and again in 2000.

For steel box girders, the girders are normally fabricated off site and lifted into place by crane, with sections connected by bolting or welding. If a composite concrete bridge deck is used, it is often cast in-place using temporary falsework supported by the steel girder. Adopted by the Army in 1925 the Large Box Girder Bridge was adaptable and relatively cheap, able to carry loads of up to 40 tonnes, it remained in service until replaced by the Bailey. This page was last edited on 2 December 2017, at 17:44. AAC was perfected in the mid-1920s by the Swedish architect and inventor Dr. The process was patented in 1924.

From “Yxhults Ånghärdade Gasbetong” later became the first registered building materials brand in the world: Ytong. Sweden in 1939 and presently licenses and owns plants in 35 locations around the world. In 1943, the first Hebel-plant was opened in Germany. In 1972, the Swedish Radiation Safety Authority pointed out the unsuitability of a radon-emitting construction material, and the use of alum slate in the production of Ytong ceased in 1975. Ytong produced a new type of aerated concrete which no longer contains alum slate and thus has eliminated the problem of radon exposure from this raw material.

The production of this white autoclaved aerated concrete is now state of the art and similar formulations are used by all producers around the world. In 1978 The Swedish team of Siporex Sweden opened the Siporex Factory in Kingdom Saudi Arabia – the “Lightweight Construction Company – Siporex – LCC SIPOREX” which have supplied the Middle east and Africa and Japan by most of its need . The LCC SIPOREX FACTORY is operating for more than 40 years . Today aerated concrete is produced by many companies, particularly in Europe and Asia.

There is some production in the Americas, and in Africa there is one plant in Egypt. AAC production in Europe has slowed down considerably, but the industry is growing rapidly in Asia due to strong demand in housing and commercial space. China is now the largest aircrete market in the world with several hundred factories. China, Central Asia, India, and the Middle-East are the biggest in terms of AAC manufacturing and consumption.

The product aircrete is sold, like other masonry materials, under many different brand names. Ytong and Hebel are brands of the international operating company Xella headquartered in Duisburg. AAC is well suited for urban areas with high rise buildings and those with high temperature variations. Due to its lower density, high rise buildings constructed using AAC require less steel and concrete for structural members. The requirement of mortar for laying of AAC blocks is reduced due to the lower number of joints. Similarly, the material required for rendering is also lower due to the dimensional accuracy of AAC.